I think the mirror would have to be large because solar energy is relatively weak. I'll try to look up the actual numbers, but I seem to recall that solar energy is somewhere on the order of approximately 1000 watts per square meter in space. Simply putting a mirror in space won't make the energy any greater. So, you'd need a large mirror to reflect a significant amount of sunlight to the ground. Pointing accuracy would have to be pretty good to aim the light at the ground station, and you'd have to allow for the Earth's (and the mirror's) rotation rate. While certainly not impossible, it's a non-trivial engineering task to develop a good (and large) mirror, fly it to space, aim it properly, and keep it in the correct position.

As for the tracking mirrors, they're certainly better than static ones. However, with a mirror at geosynch, the tracking issue isn't such a big deal. The biggest advantage of the mirror is that it could reflect light during the night (the mirror is still in daylight except during an eclipse), so you'd use the solar arrays normally during the day and use the mirror at night.

Like phil wrote, most space power satellite studies have featured large satellites in geosynch that beamed the collected energy to the ground using microwaves. The problem is that it'd take a large satellite to beam a significant amount of energy to the ground and the costs are just too high to be economically viable. Not only would the satellites themselves be expensive to build, but at roughly $10,000 per pound launch costs, they'd be very expensive to put into service. Studies back in the 1970s by Gerald O'Neal suggested that large space stations could use material harvested from the moon to build solar power satellites. Of course, that would require a very expensive infrastructure to harvest lunar materials, build the space station, equip the space station with the necessary manufacturing equipment, and operate everything. However, O'Neal believed it would be economically viable once satellite production was up to speed. This was in the days before the possibility of lunar ice at the poles was known. That ice, if it exists, could be used to produce propellant that would reduce costs even more.